Non-volatile memory

ABSTRACT

A non-volatile memory includes a substrate, a gate dielectric layer, a gate conductive layer, a nitride layer, a spacer, a first oxide layer, and a second oxide layer. The gate conductive layer, substrate and gate dielectric layer cooperatively constitute a symmetrical opening thereamong. The nitride layer has an L-shape and formed with a vertical part extending along a sidewall of the gate conductive layer and a horizontal part extending into the opening, wherein the vertical part and the horizontal part are formed as an integral structure and a height of the vertical part is below a top surface of the gate conductive layer. The spacer is disposed on the substrate and the nitride layer. The first oxide layer is disposed among the gate conductive layer, the nitride layer and the gate dielectric layer. The second oxide layer is disposed among the gate dielectric layer, the nitride layer and the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patent application Ser. No. 12/843,093 filed Jul. 26, 2010, now pending. The content of the above-mentioned patent application is hereby incorporated by reference herein in its entirety and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention generally relates to a non-volatile memory and, particularly to a non-volatile memory formed with a SONOS structure.

2. Description of the Related Art

A non-volatile memory has the advantages of the ability to perform multiple times of write, read or erase operation for data, and the stored data would not disappear after power down. The conventional non-volatile memory primarily uses polysilicon material as a charge storage layer thereof.

Owing to the characteristic of silicon nitride trapping electrons, in the conventional non-volatile memory technology, the silicon nitride is popularly used as the charge trap layer to replace a polysilicon floating gate. Generally, the silicon nitride is formed with two silicon oxides respectively disposed above and below the silicon nitride to serve as a charge tunnel layer and a charge block layer, and thereby forming a composite layer of oxide-nitride-oxide (ONO). Such type of non-volatile memory generally is termed as polysilicon/silicon oxide/silicon nitride/silicon oxide/silicon (SONOS) memory device.

According to different configuration locations of the silicon nitride charge trap layer, the SONOS memory devices can be classified into planar-type and sidewall-type. The silicon nitride charge trap layer of the planar-type SONOS memory device is disposed between two silicon oxide layers, the two silicon oxide layers are formed with two silicon layers disposed above and below the two silicon oxide layers and respectively serving as a polysilicon gate (control gate) and a silicon substrate. However, the planar-type SONOS memory device uses the ONO structure to replace the gate oxide layer and thus is incompatible with the current logic processes, and would further increase the process complexity so that the efficiency of the memory device is negatively influenced.

In addition, the silicon nitride charge trap layer of the sidewall-type SONOS memory device is disposed on the sidewall of the gate, or disposed on the sidewall of the gate and a part of the silicon substrate. Therefore, during the operation of the sidewall type SONOS memory device, electrons are necessarily required to be injected into the silicon nitride charge trap layer, which would easily encounter the issue of electron drift and influence the operation speed and charge storage capability of device.

SUMMARY

The present invention is directed to a non-volatile memory device, which can avoid of encountering issues of electron drift and would not negatively influence the efficiency of non-volatile memory, and especially can be compatible with the current logic processes, but without increasing the fabrication process complexity.

More specifically, a non-volatile memory in accordance with an embodiment of the present invention includes a substrate, a gate dielectric layer, a gate conductive layer, a nitride layer, a spacer, a first oxide layer and a second oxide layer. The gate dielectric layer is disposed on the substrate. The gate dielectric layer has a cavity formed on two end sides thereof. The gate conductive layer is disposed on the gate dielectric layer. A bottom width of the gate conductive layer is greater than a width of the gate dielectric layer. The gate conductive layer, the substrate and the gate dielectric layer cooperatively constitute a symmetrical opening thereamong. The nitride layer has an L-shape and formed with a vertical part extending along a sidewall of the gate conductive layer and a horizontal part extending into the opening. The vertical part and the horizontal part of the L-shaped nitride layer are formed as an integral structure. A height of the vertical part of the L-shaped nitride layer is below a top surface of the gate conductive layer. The spacer is disposed on the substrate as well as the nitride layer on the side of the gate conductive layer. The first oxide layer is disposed on a sidewall and bottom of the gate conductive layer as well as among the gate conductive layer, the nitride layer and the gate dielectric layer. The second oxide layer is disposed on the substrate and among the gate dielectric layer, the nitride layer and the substrate.

In one embodiment, the non-volatile memory further includes two lightly-doped regions and source/drain regions. The two lightly-doped regions are symmetrically disposed in the substrate at two sides of the nitride layer. The source/drain regions are disposed in the substrate at two sides of the spacer.

In an alternative embodiment, the non-volatile memory further includes two lightly-doped regions and source/drain regions. The two lightly-doped regions respectively are disposed in the substrate uncovered by the nitride layer, and in the substrate partially covered by the nitride layer. The source/drain regions are disposed in the substrate at two sides of the spacer.

In one embodiment, a material of the gate conductive layer is for example polysilicon or doped polysilicon.

In one embodiment, a thickness of the gate dielectric layer is in the range from 150 angstroms to 180 angstroms.

In one embodiment, a horizontal depth of the opening is in the range from 100 angstroms to 500 angstroms.

In one embodiment, the first oxide layer and the second oxide layer have a same thickness, and the thickness is in the range from 60 angstroms to 70 angstroms.

In one embodiment, the horizontal part of the nitride layer extending into the opening has a thickness in the range from 30 angstroms to 40 angstroms.

In one embodiment, the spacer completely covers the L-shaped nitride layer.

Owing to the present embodiments do not adopt the conventional solution of replacing the gate dielectric layer by the ONO structure, the present embodiments can be compatible with the current logic process and would not influence the efficiency of device. In addition, in the non-volatile memory of the present invention, a part of the nitride layer (charge trap layer) is formed between the gate conductive layer and the substrate, so that can avoid encountering the problem of electron drift and would not influence the operation speed and charge storage capability of device, and further can achieve relatively high efficiency of programming/erasing at low operation voltage. Moreover, the manufacturing method of the present invention would not increase the amount of photo mask and thus would not increase the process complexity.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:

FIG. 1 is a schematic cross-sectional view of a non-volatile memory in accordance with an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a non-volatile memory in accordance with another embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a non-volatile memory in accordance with still another embodiment of the present invention.

FIGS. 4A through 4H are process cross-sectional views of a manufacturing method of a non-volatile memory in accordance with an embodiment of the present invention.

FIGS. 5A through 5E are process cross-sectional views showing integration of a current logic process and a non-volatile memory in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

A better understanding of the above and many other features and advantages of the novel non-volatile memory and manufacturing method thereof of the present invention may be obtained from a consideration of the detailed description of some exemplary embodiments thereof below, particularly if such consideration is made in conjunction with the appended drawings, wherein like reference numerals are used to identify like elements illustrated in one or more of the figures thereof.

FIG. 1 illustrates a schematic cross-sectional view of a non-volatile memory in accordance with an embodiment of the present invention.

As illustrated in FIG. 1, a non-volatile memory 100 includes a substrate 101, a gate dielectric layer 102, a gate conductive layer 104, a first oxide layer 106, a nitride layer 110 and a second oxide layer 108. The substrate 101 is, for example, a silicon substrate. The gate dielectric layer 102 is disposed on the substrate 101. The gate dielectric layer 102 has a cavity 103 formed on two end sides thereof. The gate dielectric layer 102 is, for example, a silicon oxide layer. The gate dielectric layer 102 has a thickness, for example, in the range from 150 angstroms to 180 angstroms.

The gate conductive layer 104 is disposed on the gate dielectric layer 102. A bottom width of the gate conductive layer 104 is greater than a bottom width of the gate dielectric layer 102. Moreover, the gate conductive layer 104, the substrate 101 and the gate dielectric layer 102 cooperatively constitute a symmetrical opening 105. A horizontal depth of the opening 105 is, for example, about 200 angstroms, and is preferably in the range from 100 angstroms to 500 angstroms. The gate conductive layer 104 is made of, for example, polysilicon or doped polysilicon, and serves as a control gate of the non-volatile memory 100.

The nitride layer 110 of the non-volatile memory 100 serves as a charge trap layer of memory device for storing charges. The nitride layer 110 is disposed on a sidewall of the gate conductive layer 104, and extended into the opening 105. As shown in FIG. 1, the nitride layer 110 has an L-shape, and is formed comprising a vertical part 110 a extending along the sidewall of the gate conductive layer 104 and a horizontal part 110 b extending into the opening 105. In addition, a height of the vertical part 110 a of the (L-shaped) nitride layer 110 is below or lower than a top surface of the gate conductive layer 104. A material of the nitride layer 110 is, for example, silicon nitride. A thickness of the horizontal part 110 b of the nitride layer 110 extending into the opening 105 is, for example, in the range from 30 angstroms to 40 angstroms.

The first oxide layer 106 is disposed among the gate conductive layer 104, the nitride layer 110 and the gate dielectric layer 102, and also is formed on the sidewall and the bottom of the gate conductive layer 104. A material of the first oxide layer 106 is, for example, silicon oxide. A thickness of the first oxide layer 106 is, for example, in the range from 60 angstroms to 70 angstroms. The second oxide layer 108 is disposed among the substrate 101, the gate dielectric layer 104 and the nitride layer 110, and also is formed on the substrate 101. A material of the second oxide layer 108 is, for example, silicon oxide. A thickness of the second oxide layer 108 is for example in the range from 60 angstroms to 70 angstroms.

The second oxide layer 108 and the first oxide layer 106 of the non-volatile memory 100 serve as a charge tunnel layer and a charge block layer, respectively. The second oxide layer 108, the first oxide layer 106 and the nitride layer 110 cooperatively constitute an oxide-nitride-oxide (ONO) structure, and the gate conductive layer 104, the ONO structure and the substrate 101 together as a whole are termed as a SONOS (i.e., generally polysilicon-oxide-nitride-oxide-silicon) memory.

It is noted that, compared with a conventional planar type SONOS memory using an ONO structure to replace the gate dielectric layer, the ONO structure of the present embodiment would not negatively affect the fabrication of the gate dielectric layer, and thus can relatively reduce the process complexity.

In addition, in the non-volatile memory associated with the present invention, the gate conductive layer 104 and the substrate 101 have a part or portion of the nitride layer 110 disposed therebetween. Therefore, compared with a conventional sidewall type SONOS memory, the non-volatile memory of embodiments of present invention can avoid encountering the issue of electron drift and thus would not negatively affect the operation speed and charge storage capability of the memory device.

Referring to FIG. 2, which illustrates a schematic cross-sectional view of a non-volatile memory in accordance with another embodiment of the present invention.

As illustrated in FIG. 2, the non-volatile memory 100 further includes two lightly-doped regions 112, 114, a spacer 117 and a plurality of source/drain regions 120 located or disposed besides the structural elements illustrated in FIG. 1. The lightly-doped region 114 is disposed in the substrate 101 at a side of the nitride layer 110. The lightly-doped region 112 is disposed in the substrate 101 below the nitride layer 110 and extending to the other side of the nitride layer 110.

Furthermore, it is illustrated in FIG. 2 that the spacer 117 completely covers the (L-shaped) nitride layer 110, and is disposed on the sidewall of the gate conductive layer 104 as well as being disposed on the substrate 101. The spacer 117 is, for example, a composite material layer which includes a silicon oxide 116 and a silicon nitride 118. The source/drain regions 120 are respectively disposed in the substrates 101 at two opposite sides of the spacer 117.

The lightly-doped region 112 and the lightly-doped region 114 of the illustrated embodiment of the non-volatile memory 100 constitute two asymmetrical lightly-doped regions, and as a whole, can be used for storing single-byte data.

Referring to FIG. 3, which illustrates a schematic cross-sectional view of a non-volatile memory in accordance with a still another embodiment of the present invention. As illustrated in FIG. 3, a difference between a non-volatile memory 100 a and the non-volatile memory 100 as illustrated in FIG. 2 is the following: a lightly-doped region 112 a and an another lightly-doped region 114 a of the non-volatile memory 100 a are symmetrically disposed in the substrates 101 at two sides of the nitride layer 110, and as a whole, can be used for storing two-byte data.

In the following descriptions, a manufacturing method of a non-volatile memory in accordance with an embodiment of the present invention will be described in detail. Specifically, FIGS. 4A through 4H illustrate process cross-sectional views of an exemplary manufacturing method of a non-volatile memory of the embodiment of present invention.

Firstly, as illustrated in FIG. 4A, a substrate 400 is provided. The substrate 400 is, for example, a silicon substrate. A gate dielectric material layer 402 then is formed on the substrate 400. The gate dielectric material layer 402 is, for example, made of silicon oxide. A formation method of the gate dielectric material layer 402 is for example a thermal oxidation method. A thickness of the gate dielectric material layer 402 is, for example, in the range from 150 angstroms to 180 angstroms.

Afterwards, still referring to FIG. 4, a gate conductive material layer 404 is formed on the gate dielectric material layer 402. A material of the gate conductive material layer 404 is for example polysilicon or doped polysilicon. A formation method of the gate conductive material layer 404, for example, includes the following: a chemical vapor deposition process is used to form an un-doped polysilicon layer and then an ion implantation process is performed, or a chemical vapor deposition process cooperative with an in-situ implantation of dopant is used.

Subsequently, as illustrated in FIG. 4B, the gate conductive material layer 404 and the gate dielectric material layer 402 are patterned to form a gate structure 406. The gate structure 406 includes a gate conductive layer 405 and a gate dielectric layer 403. The gate conductive layer 405 serves as a control gate. The method of patterning includes for example that the following steps: firstly forming a patterned photoresist layer (not shown) on the gate conductive material layer 404, then taking the patterned photoresist layer as a mask to perform an etching process for partly removing the gate conductive material layer 404 and the gate dielectric material layer 402, and thereby forming the gate structure 406 consisted of the gate conductive layer 405 and the gate dielectric layer 403. Afterwards, the patterned photoresist layer is removed.

Referring to FIG. 4C, the gate dielectric layer 403 is partly removed to form a cavity 408 on two end sides of the gate dielectric layer 403. Moreover, after the gate dielectric layer 403 is partly removed, a symmetrical opening 410 is formed among the gate conductive layer 405, the substrate 400 and the gate dielectric layer 403. A horizontal depth of the opening 410 is, for example, about 200 angstroms and preferably in the range from 100 angstroms to 500 angstroms. Herein, a method for partly removing the gate dielectric layer 403 is for example performing a wet etching process or a dry etching process.

Referring to FIG. 4D, a first oxide layer 412 is formed on a sidewall and bottom of the gate conductive layer 405, and a second oxide layer 414 is formed on a top surface of the substrate 400. A formation method of the first oxide layer 412 and the second oxide layer 414 is, for example, as follows: performing an oxidation process 411 to simultaneously form the first oxide layer 412 and the second oxide layer 414 on the gate conductive layer 405 and the top surface of the substrate 400. The oxidation process 411 is for example a thermal oxidation process, and a process temperature thereof is, for example, lower than 800 Celsius degrees. A material of the first and second oxide layers 412, 414 is, for example, silicon oxide, and a thickness thereof is, for example, in the range from 60 angstroms to 70 angstroms.

Referring to FIG. 4E, a nitride material layer 416 is formed to be covering the gate structure 406, the first oxide layer 412, the second oxide layer 414 and the substrate 400. The nitride material layer 416 also is filled into the opening 410. A formation method of the nitride material layer 416 is, for example, a low pressure chemical vapor deposition process, and a material thereof is, for example, silicon nitride.

Referring to FIG. 4F, an etching process is performed to partly remove the nitride material layer 416 and thereby forming a nitride layer 418. Especially, the nitride layer 418 is formed on the sidewall of the gate conductive layer 405 and further extending into the opening 410 as an L-shaped integral structure. A thickness of the extension portion of the nitride layer 110 is for example in the range from 30 angstroms to 40 angstroms.

Referring to FIG. 4G, a doping process is performed to form two lightly-doped regions 420, 422 in the substrate 400. The lightly-doped region 420 is formed in the substrate 400 at a side of the nitride layer 418, and the lightly-doped region 422 is formed in the substrates 400 below the nitride layer 418 and extending to another side of the nitride layer 418. A formation method of the lightly-doped region 422 is, for example, including the following: after performing the doping process, using a tilt-angle implanting method to make the lightly-doped region extend to the channel below the nitride layer 418.

In another embodiment, the two lightly-doped regions can be symmetrically formed in the substrates 400 at two sides of the nitride layer 418 instead.

Referring to FIG. 4H, after the formation of the lightly-doped regions 420, 422, several processes for forming a spacer 427 and source; drain regions 428 can be subsequently performed. In the illustrated embodiment, the spacer 427, completely covering the L-shaped nitride layer 418, is, for example, a composite layer consisted of a silicon oxide layer 424 and a silicon nitride layer 426. Methods for forming the spacer 427 and the source/drain regions 428 can adopt conventional methods, and thus will not be repeated herein.

As seen from the above descriptions, the present manufacturing method of a non-volatile memory does not completely replace the gate dielectric layer with the ONO structure and thus is different from the conventional method taught in the prior art. Accordingly, the present manufacturing method can be compatible with the current logic processes, and thus would not influence the efficiency of the logic device.

In the present manufacturing method, by etching the gate dielectric layer to facilitate a part of the nitride layer to be formed between the gate conductive layer and the substrate, and utilizing the oxidation process to simultaneously form the oxide layers on the top and bottom of the nitride layer, the ONO structure is formed consequently. Accordingly, the present manufacturing method would not increase the amount of photo mask, and thus would not increase the process complexity, and furthermore, would not encounter the issue of electron drift.

In the following, an integration process of the present manufacturing method of a non-volatile memory and a current logic process will be described in detail.

FIGS. 5A through 5E illustrate process cross-sectional views of integration of a current logic process and a non-volatile memory in accordance with another embodiment of the present invention.

Firstly, as illustrated in FIG. 5A, a substrate 500 defined with a logic device region 502 and a memory region 504 is provided, and a gate dielectric material layer 506 and a gate conductive material layer 508 are sequentially formed on the substrate 500.

Referring to FIG. 5B, a covering layer (not shown) is firstly formed on the gate conductive material layer 508 in the logic device region 502 of the substrate 500. Afterwards, the gate conductive material layer 508 and the gate dielectric material layer 506 in the memory region 504 are patterned, and whereby forming a gate conductive layer 508 a and a gate dielectric layer 506 a.

Referring to FIG. 5C, after the gate conductive material layer 508 and the gate dielectric material layer 506 in the memory region 504 are patterned, processes of forming a gate dielectric layer 506 b, a first oxide layer 510, a second oxide layer 512, a nitride layer 514 and lightly-doped regions 516, 518 are performed. The formation methods of the gate dielectric layer 506 b, the first oxide layer 510, the second oxide layer 512, the nitride layer 514 and the two lightly-doped regions 516, 518 can be the same as those previously-described in the above-mentioned manufacturing method of a non-volatile memory, and thus will not be repeated herein.

It is understood that, after finishing the above manufacturing process of the non-volatile memory, a general logic process can be subsequently performed. In particular, the covering layer (not shown) in the logic device region 502 is removed, and another covering layer (not shown) will be formed in the memory region 504. Afterwards, the gate conductive material layer 508 and the gate dielectric material layer 506 in the logic device region 502 is patterned to form a gate conductive layer 508 b and a gate dielectric layer 506 c (as shown in FIG. 5D).

Referring to FIG. 5E, the covering layer in the memory region 504 is removed. A spacer 516 and source/drain regions 518 then are simultaneously formed in each of the logic device region 502 and the memory device region 504.

Subsequently, the memory structure as illustrated in FIG. 2 is taken as an example to illustrate an operation method of the non-volatile memory in accordance with the present invention.

Referring back to FIG. 2, the operation method of the non-volatile memory 100 is as follow: during programming, the one on the right hand side (referred herein as the right one) of the source/drain regions 120 is applied with a bias-voltage for example about +3V˜+5V, the one on the left hand side (referred herein as the left one) of the source/drain regions 120 is applied with a bias-voltage of, for example, 0V, the gate conductive layer 104 is applied with a bias-voltage of, for example. +6V, and the substrate 101 is applied with a bias-voltage of, for example, 0V or about −1˜−2V, so that electrons can be injected into the nitride layer (charge trap layer) 110 adjacent to the right one of the source/drain regions 120 by channel hot electron injection.

During erasing, the right one of the source/drain regions 120 can be applied with a bias-voltage for example of about +3V˜+5V, the left one of the source/drain regions 120 is applied with a bias-voltage of, for example. 0V, the gate conductive layer 104 is applied with a bias-voltage for example of −6V, and the substrate 101 is applied with a bias-voltage of, for example, 0V, which facilitates to erase the previously stored data by a Fowler-Nordheim (F-N) tunneling effect or a band to band hot hole injection.

In addition, during reading, the right one of the source/drain regions 120 can be applied with a bias-voltage for example of 0V, the left one of the source/drain regions 120 is applied with a bias-voltage for example of 1.5V, the gate conductive layer 104 is applied with a positive bias-voltage, and the substrate 101 is applied with a bias-voltage for example of 0V, which facilitates to read the data stored in the non-volatile memory 100.

Since in the device structure of the present non-volatile memory, a part of the nitride layer (charge trap layer) is formed between the gate conductive layer and the substrate, therefore, compared with the conventional non-volatile memory, the ONO structure of the present non-volatile memory in accordance with the embodiments of present invention can produce a relatively strong perpendicular electric field and thus can achieve relatively high efficiency of programming/erasing at lower or reduced operation voltage.

In summary, the non-volatile memory and the manufacturing method thereof in accordance with the embodiments of the present invention at least can achieve the following advantages of (1)-(4).

(1), the present invention can be compatible with the current logic process, relatively reduce the process complexity and would not negatively influence the efficiency of logic device.

(2), the present invention can avoid encountering the issue of electron drift and would not influence the operation speed and charge storage capability of device.

(3), the manufacturing method of the present invention would not increase the amount of photo mask, and thus would not cause the process to be complicated.

(4), the non-volatile memory of the present invention can achieve relatively high efficiency of programming/erasing at low operation voltage.

The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein, including configurations ways of the recessed portions and materials and/or designs of the attaching structures. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments. 

What is claimed is:
 1. A non-volatile memory comprising: a substrate; a gate dielectric layer, disposed on the substrate and having a cavity formed on two end sides of the gate dielectric layer; a gate conductive layer, disposed on the gate dielectric layer and having a bottom width greater than a width of the gate dielectric layer, wherein the gate conductive layer, the substrate and the gate dielectric layer cooperatively constitute a symmetrical opening thereamong; a nitride layer, having an L-shape and formed with a vertical part extending along a sidewall of the gate conductive layer and a horizontal part extending into the opening, wherein the vertical part and the horizontal part are formed as an integral structure and a height of the vertical part of the L-shaped nitride layer is below a top surface of the gate conductive layer; a spacer, disposed on the substrate as well as the nitride layer on the side of the gate conductive layer; a first oxide layer, disposed on a sidewall and bottom of the gate conductive layer and among the gate conductive layer, the nitride layer and the gate dielectric layer; and a second oxide layer, disposed on the substrate and among the gate dielectric layer, the nitride layer and the substrate.
 2. The non-volatile memory as claimed in claim 1, further comprising: two lightly-doped regions, symmetrically disposed in the substrate at two sides of the nitride layer; and source/drain regions, disposed in the substrate at two sides of the spacer.
 3. The non-volatile memory as claimed in claim 1, further comprising: two lightly-doped regions, respectively disposed in the substrate uncovered by the nitride layer, and in the substrate partially covered by the nitride layer; and source/drain regions, disposed in the substrate at two sides of the spacer.
 4. The non-volatile memory as claimed in claim 1, wherein a material of the gate conductive layer comprises polysilicon or doped polysilicon.
 5. The non-volatile memory as claimed in claim 1, wherein a thickness of the gate dielectric layer is in the range from 150 angstroms to 180 angstroms.
 6. The non-volatile memory as claimed in claim 1, wherein a horizontal depth of the opening is in the range from 100 angstroms to 500 angstroms.
 7. The non-volatile memory as claimed in claim 1, wherein the first oxide layer and the second oxide layer have a same thickness, and the thickness is in the range from 60 angstroms to 70 angstroms.
 8. The non-volatile memory as claimed in claim 1, wherein the horizontal part of the nitride layer extending into the opening has a thickness in the range from 30 angstroms to 40 angstroms.
 9. The non-volatile memory as claimed in claim 1, wherein the spacer completely covers the L-shaped nitride layer. 